Analyzing an inorganic sample via analytical techniques such as x-ray fluorescence (XRF), inductively coupled plasma (ICP), atomic absorption (AA) requires that the sample be specially prepared before analysis. The sample must often be in the form of a homogeneous, solid, smooth-surface shape, such as that of a disk or bead. In this form, the sample does not exhibit mineralogical, grain-size, or orientation effects that might otherwise skew the analytical results.
A process known as “fusion” can be used to prepare samples for XRF, ICP, and AA. During the fusion process, a powdered sample is dissolved in a solvent, typically a lithium borate flux. The flux is solid at room temperature and must therefore be liquefied, which typically occurs at high temperature (c.a. 900 to 1000° C.).
As a consequence of the high temperatures required, the fusion process is performed in a heater/furnace/burner. Energy for the process is supplied either by gas (i.e., a gas burner) or electricity (i.e., an electric heater or furnace). Electrically powered furnaces can be inductive or resistive.
The heater or furnace, along with other control circuitry, etc., is contained with a larger enclosure; the assemblage is typically called a “fluxer”.
“Platinumware” holders, including a “crucible holder” and a “mold holder” or “mold rack” are used in conjunction with the fluxer. The moniker “platinumware” derives from the fact that the crucibles and molds are typically made of platinum. FIG. 1 and FIG. 2 depict respective prior-art crucible holder 100 and mold rack 200, as used in some resistive-heated furnaces available from Katanax, Inc. of Québec, Canada. The platinumware holders are arranged to move in and out of the hot zone (i.e., furnace or burner flame) under the control of a motor/actuator.
Crucible holder 100 is capable of supporting plural crucibles 112. In the embodiment shown, crucible holder 100 is designed to accommodate five crucibles 112. As depicted in FIG. 1, crucible holder 100 includes support beam 102, spacers 104, retaining beams 106, brackets 108, and end shafts 110, arranged and interrelated as shown. Mold rack 200 is capable of supporting plural molds 224, which is typically consistent with the number of crucibles 112 in the crucible holder. Mold rack 200 includes support beams 214, mold retainers 216, spacers 218, brackets 220, and end supports 222, arranged and interrelated as shown.
In use, crucible holder 100 is disposed above molder holder 200. Crucible holder is supported so as to be rotatable about its longitudinal axis (i.e., an axis that aligns with the two end shafts 110). Crucibles 112 and molds 224 are situated to align with one another so that hot solution poured from each crucible 112 is received by a respective mold 224.
To begin the fusion process, the flux and sample are deposited into crucibles 112, which are then moved into the furnace cavity to begin the fusion process. See, e.g., http://www.katanax.com/cgi/show.cgi?products/K2prime/K2primevideo.I=en.html.
After the flux is liquefied, and after complete dissolution of the sample, the molten solution in the crucible(s) is poured into the plate-shaped platinum mold(s). Cooling results in a small, homogeneous glass-like disk or bead of sample, now suitable for analysis.
The throughput required of a fluxer will of course vary from one customer/lab/site (hereinafter “site”) to another. And the requirements at a given site can change over time. In particular, with the increasing popularity of the fusion technique, it is likely that a site will see their fusion demands increase over time. Although some gas-fired fluxers are designed with a larger casing to accommodate a variable number of burners, no electrical fluxer offers this flexibility.
In particular, when designing gas fluxers, it is relatively easy to provide a manifold with multiple gas outputs, each one capable of functioning as a fusion position. To reduce the number of fusion positions, one or more of the gas outputs are capped or plugged. To increase the number of fusion positions, one or more burners are coupled to the gas outputs. The burners are typically positioned quite close one to another, so there is not much cost to providing the potential for a large capacity, even if a number of the fusion positions remain unused.
The issue of spare capacity is more complicated with electric fluxers. If a large furnace is built, all heating elements must be operated to provide the requisite heating, even if only a few samples are being processed such that spare capacity remains. Alternatively, a fluxer could be designed to accommodate several individual furnaces situated adjacent to one another. But since each furnace requires several inches of insulation, when positioned side-by-side, the thickness of the (insulated) side walls widens the fluxer to an unacceptable size.
To satisfy increasing fusion demands, it is advantageous to conduct the fusion process as quickly as possible. This implicates the fluxer's temperature response; that is, the relative speed with which it is capable of changing temperature and stabilizing at temperature targets. Despite its many benefits, a perceived drawback of a typical electric fluxer is that its temperature cannot vary as quickly as that of a gas fluxer.
As a consequence, there is a need for an electric fluxer that can accommodate an increase in the number of fusion positions (i.e., the number of simultaneous samples that can be accommodated per run). This would enable an initial modest throughput to be increased without having to purchase a new fluxer. Furthermore, there is a need for an electric fluxer with increased temperature responsivity, which will speed the fusion process thereby increasing throughput.